This invention relates to an automatic document feeder with a document reversing function which is mounted on an electrophotographic copier, wherein a two sides document is conveyed in both ordinary and reverse directions on the platen glass to be exposed on both sided of the document. Automatic document feeders (ADF) have previously been provided for electrophotographic copiers and image reading apparatus in order to supply documents to them effectively and automatically, but conventional automatic document feeders have a limited function in that they are used mainly for copiers which can copy only one sided documents.
Recently there are great necessities for a copier which can copy two sided documents onto one side or both sides of a recording paper, and for an image reading apparatus to read and record both sides of the document. As a result, a lot of reversible automatic document feeders (RADF) which are equipped with a document reversing mechanism, have been proposed. Those are disclosed in Japanese Patent Publication Open to Public Inspection No. 216159/1984, Japanese Patent Publication Open to Public No. 112738/1978, Japanese Patent (Utility Model) Open to Public Inspection No. 4548/1984, and Japanese Patent Publication Open to Public Inspection No. 8834/1985.
A circulation type document feeder (RDH) has also been proposed. It is a document feeder in which a document sheet is separated from a pile of document sheets on a document stacker, fed automatically onto a platen glass sheet by sheet, exposed on the platen glass, and returned to the document stacker to be processed repeatedly. This circulation type document feeder (RDH) can make one copy at each circulation, so a document sheet is circulated in the document feeder as many times as the necessary number of copies.
A circulation type document feeder in which a mechanism is installed to turn over documents, was proposed by the inventors of the present invention recently. It is disclosed in Japanese Patent Application No. 20228/1988. This document feeder makes the following possible. Copying can be conducted continuously and rapidly, copied recording sheets can be sorted promptly and also be finally processed without an operator by being connected with a finishing unit which conducts stapling, punching, and so forth.
In this document feeder with the document turning- over function, documents are piled on the stacker with their front sides upwards and the bottom document of the pile is separated from the pile and conveyed onto the platen glass sheet by sheet.
The operation of the document conveyance unit of the document feeder will be explained as follows. (1) A document is conveyed by normal rotation of the conveyance belt onto the platen glass through a conveyance path. When the trailing edge of a document is detected by a trailing edge detecting sensor, the document stops for a while. (2) The document proceeds to a document turn-over path by the reverse rotation of the conveyance belt without being exposed. (3) Then the document is conveyed onto the platen glass again and the reverse side of the document is exposed. (4) After exposure, the document is conveyed through the path of the document turning-over mechanism. (5) The document is conveyed onto the platen glass and the front side of the document is exposed. (6) After both sides of the document are exposed, this two sided document is returned onto the top of the pile of documents on the stacker.
In this circulation type document feeder which can process two sided documents, there are some problems which will be described below. After the trailing edge of the document was detected passing through in step (1) mentioned above, the document will be conveyed in the reverse direction as in step (2) mentioned above. At this moment, a small size document, such as a `B5` document of Japanese Standard Size, is not completely compressed by a conveyance belt or a roller. Therefore, the force to convey the document to the document turn-over mechanism is not strong enough. So, some problems occur such as skewing of document, no feeding of document, jamming of document, and so forth.